Infrared imaging is widely used in a variety of applications including night vision, surveillance, search and rescue, remote sensing, and preventive maintenance. Imaging devices for these applications, which must be able to detect near, mid and far infrared light, are typically constructed from InGaAs, InSb and HgCdTe focal plane arrays. Such arrays are complicated to manufacture and costly.
Alternatively, quantum well infrared photodetectors (QWIPs) can detect mid and far infrared light. QWIP devices are described in U.S. Pat. No. 4,873,555, issued Oct. 10, 1989 to the University of Pittsburgh and in U.S. Pat. No. 4,894,526 issued Jan. 16, 1990 to American Telephone and Telegraph Company, AT&T Bell Laboratories. The latter patent describes a QWIP device which utilizes a series of quantum wells and thus has a better efficiency.
Infrared thermal imaging, which incorporates GaAs QWIPs and GaAs LEDs (Light Emitting Diodes) via epitaxial growth integration, was disclosed by H. C. Liu, in U.S. Pat. No. 5,567,955 issued Oct. 22, 1996 and in U.S. Pat. No. 6,028,323 issued Feb. 22, 2000, both to the National Research Council of Canada and which are incorporated herein by reference. The former patent describes the vertical integration of a light emitting diode with a QWIP.
Current from the QWIP device resulting from the impingement of far-infrared (FIR) light on the photodetector drives the LED to emit near infrared (NIR) energy. This energy can be efficiently detected by a low-cost silicon CCD (Charge Coupled Device), leading to a highly efficient detector. The device described in U.S. Pat. No. 5,567,955 requires a substantially transparent substrate. This requirement is no longer necessary for the devices described in U.S. Pat. No. 6,028,323, in which the input FIR energy is launched into a same side (face) of the device from which the up-converted NIR energy is collected.
U.S. Pat. No. 6,028,323 described devices that can be used as a pixelless means of up-converting and imaging a FIR beam to a NIR beam, presented device and system configurations that allows the input FIR energy and output NIR energy through the same side of the device, and elucidated measures that minimizes the blurring and smearing effects.
In both aforementioned patents, the vertical device integration relies on subsequent epitaxial growth of the LED layers over the QWIP layers on a same substrate.
Recently, an InGaAs/InP based p-i-n photodetector (PD) operating at a peak wavelength of 1.5 μm has been integrated with a GaAs-based LED in the near infrared region, as reported by Ban et al. The operation principle is as following. The structure of the device is a back-to-back p-i-n PD and LED, with a common p-region in the middle. Under normal operation conditions, the PD is reverse biased and the LED is forward biased. Incident infrared light (with peak wavelength at 1.65 μm or shorter), shone onto the back of the device, is absorbed by the In0.53Ga0.47As PD. The resulting photocurrent drives the LED to emit at 0.87 μm, which is collected from the device top surface. The In0.53Ga0.47As/InP PD was grown by metal organic chemical vapor deposition (MOCVD) on an n-type InP substrate. The GaAs/AlGaAs LED structure was grown by molecular beam epitaxy (MBE) on an n-type GaAs substrate. The two wafers were bonded together via wafer fusion.
Wafer fusion is an advanced processing technology that allows the integration of heterogeneous semiconductor materials regardless of their lattice constants. It removes the limitations associated with the use of lattice-matched materials and gives a new degree of freedom for the design of semiconductor optoelectronic devices. Wafer fusion is described, for example, in Yang et al. in Appl. Phys. Lett., Vol. 79, pp. 970–972, 2001; Karim et al. in Appl. Phys. Lett., Vol. 78, pp. 2632–2634, 2001; Tan et al. in J. Electron. Materials, Vol. 29, pp. 188–194, 2000; and Levine et al. in Appl. Phys. Lett., Vol. 75, pp. 2141–2143, 1999, the contents of which are herein incorporated by reference. Wafer fusion can be simply described as a direct bonding in which chemical bonds are established between two wafers/materials at their hetero-interface in the absence of an intermediate layer.